1. Technical Field
The present invention relates to an antenna unit.
2. Related Art
Wireless communications devices are equipped with an antenna unit for transmission and reception of radio waves to and from other wireless communications devices. In antenna units of this kind, it is preferable for example for the orientation of the antenna provided to the antenna unit to be maintained in the direction of gravity in order to provide good transmission and reception of vertically polarized waves. Additionally, it is preferable for the orientation of the antenna provided to the antenna unit to be maintained in the horizontal direction (the direction orthogonal to the direction of gravity) in order to provide good transmission and reception of horizontally polarized waves.
Various techniques were proposed in the past for achieving good transmission and reception of radio waves in antenna units. For example, a mobile communications device with an internal antenna is provided with antenna retaining means for maintaining orientation of the antenna in the direction of gravity despite changes in orientation of the mobile communications device, thereby reducing the decline in reception of radio waves associated with changing orientation of the mobile communications device.
However, according to the above technique, because the support shaft of the antenna is disposed at a location away from the center axis of the antenna, and this support shaft is secured to the interior of the mobile communication device, it was not possible to maintain the orientation of the antenna in the direction of gravity when the orientation of the mobile communications device changed in the direction of revolution centered on an axis that is orthogonal to this support shaft.
Additionally, as wireless LANs (Local Area Networks) have become widespread, antenna unit-equipped mobile communications devices of a type designed for example to be used indoors on a desktop have become increasingly common. Mobile communications devices of this type are typically used either in so-called “transverse orientation” or “longitudinal orientation”, so the orientation of the antenna of the antenna unit does not change frequently with respect to the direction of gravity. Thus, for this type of antenna unit, the above technique is not essential.
If a mobile communications device designed to be used in transverse orientation or in longitudinal orientation is furnished with a polarization diversity antenna system, good transmission and reception of radio waves is afforded regardless of whether the mobile communications device is used in transverse orientation or used in longitudinal orientation. However, some types of antenna units can not equip with the polarization diversity antenna system because of its circuit configuration.
An advantage of some aspects of the invention is to provide a novel technique relating to an antenna unit that affords good reception and/or transmission of prescribed polarized waves, even when the orientation of the antenna unit with respect to the direction of gravity changes.
The entire disclosure of Japanese patent application No. 2009-102563 of BUFFALO is hereby incorporated by reference into this document.